In inkjet recording, a coloured dye or coloured pigment dispersed, in an aqueous or non-aqueous solvent, is extruded as minute fine drops from one or more nozzles, and the liquid drops are made to form a desired character or image by electronic control on the recording medium.
As a recording medium employing this recording method, paper used for electrostatic transfer or ordinary paper used for writing can be used, but to obtain a good recorded image, the recording medium must have the following two sets of characteristics. The first set of characteristics is good ink absorption, ink drops adhering to the surface of the medium rapidly penetrate the interior of the medium, the image rapidly develops a dry appearance, and the image does not smudge on contact with the recording device, another medium or the hands. The second set of characteristics is that ink drops do not diffuse through the interior or surface of the medium more than is necessary, and dots recorded by the ink drops do not become too large or assume a distorted shape.
The coloured components used in the ink may be direct dyes, acidic dyes, basic dyes, reactive dyes, dispersion dyes or various pigments. Water-soluble dyes are most often used, but in the case of inkjet recording, there is usually a very serious problem insofar as the recorded image has poor water resistance. For example, when an image recorded by the inkjet recording method is taken outdoors, it may occur that of the image smudges due to rain and the recorded image can no longer be read. Alternatively, if the image is left for a long period of time under high humidity conditions, it may smudge and spoil the image quality.
Hence, to make the recorded image from inkjet recording water resistant, in Tokkai Sho 55-150396 (Koho), an invention is proposed wherein, after printing is performed using a water-based dye ink, a reagent is used which forms a lake with the dye to confer water resistance.
Various compounds that are ink water resistance-conferring agents and which can be first added to the ink-receiving layer of the inkjet recording medium, are also known. For example, JP,56-59239. (Koho) proposes a polycation polyelectrolyte, JP,61-68788 (Koho) proposes a weak acid salt of a polyallylamine, JP,60-49990 (Koho) proposes an ammonium polyalkylene polyamine dicyandiamide, JP,1-157884 (Koho) proposes chitosan, JP,6-92011 (Koho) proposes cation denaturation colloidal silica, while JP,6-92012 (Koho) proposes a copolymer of dimethylamine and epichlorohydrin, these compounds being added to the ink-receiving layer beforehand.
Besides the above-mentioned compounds, cationic resins such as dicyandiamide formaldehyde resin, diethylenetriamine dicyandiamide ammonium chloride condensate, (meta)acryloyloxy-alkyl trialkylammonium chloride polymer, dimethyl diallylammonium chloride polymer, ethyleneimine polymers, diallylamine polymers and ammonia/epichlorohydrin/dimethylamine copolymers, are already known as an ink water resistance-conferring agents.
It is known that the aforementioned water-soluble cationic resins form complexes by bonding to anionic water-soluble direct dyes, acidic dyes, reactive dye, etc., thereby increasing the water resistance of water-soluble paints and preventing decoloring of yarn, cloth, etc. dyed with water-soluble paints.
However, if a solvent such as water is present in the environment when a complex with a dye molecule is made, the complex will displace easily from the dyed object, so these water-soluble cationic resins apparently have a low waterproofing effectiveness, and even if they were used as an ink jet recording medium, they did not give satisfactory recording quality.
It is therefore a first object of this invention to provide an additive having a cationic resin as its principal component which has a large effectiveness in improving the waterproof properties of an image colored or recorded with a water soluble dye. It is a second object of this invention to provide a recorded medium suitable for multicolor recording by the ink-jet recording method which not only addresses the problem of inadequate waterproofness of recorded characters and images, which was the defect of conventional inkjet recording media, but also improves resolution and color tone, provides a high resolution similar to that of a silver salt photograph, and gives little difference of hue of recorded characters or images compared to the hue of the dyes themselves which are currently used in ink.